East-Central and Southeast Iowa Crop
Information

I have been getting a number
of calls related to soybeans that have cupped up or have malformed leaves that
look like dicamba or growth regulator herbicide
injury. When this problem occurs, the possibility of spray drift needs to be
investigated. If an herbicide has drifted from a nearby corn field or roadside,
the symptoms should be greatest near the source of the drift and gradually
diminish with a greater distance from the source. Also the symptoms should be
less near anything that would have obstructed the drift, such as tall grass or
trees. If a drift pattern is not evident, then it is unlikely to be the reason
for the symptoms.

If the symptoms appear after a field is sprayed and there is a
sprayer pattern to the symptoms, the possibility of sprayer contamination with dicamba (Banvel, Clarity, Northstar, Distinct) or another
growth regulator herbicide should be investigated. However, we do occasionally
see these symptoms in the absence of a growth regulator herbicide. Occasionally
additives, such as ammonium sulfate (AMS), 28% Nitrogen solution, or
surfactants can cause these symptoms. I have also seen symptoms not show up
until 2 or more weeks after the field is sprayed. If dicamba
was the source of the problem, symptoms should show up within a day or two.

In some cases the entire field showed the problem before anything was
sprayed on the field or in neighboring fields. Sometimes the symptoms are
uniform across the entire field and sometimes certain parts of the field are
worse than others, but there is no drift pattern. I see this most often when
the soybeans go through a growth spurt when temperatures are high after some
cool weather or after a heavy rainfall. Apparently under these conditions, the
balance of naturally occurring hormones in the plant is disrupted, resulting in
symptoms characteristic of growth regulator herbicide damage. Usually the
soybeans recover from this condition with little to no effect on the final
yield. See the July 19, 1999 ICM Newsletter for more information (http://www.ipm.iastate.edu/ipm/icm/1999/7-19-1999/malsoy.html).

Asian Soybean Rust

Soybean rust has been
detected on sentinel plots in central Louisiana,
which is the furthest north so far this year. This is near the area which
was the source of the inoculum for the northward movement
of the disease last September, so we need to keep an eye on the south. See http://sbrusa.net/
for the latest info.

Soybean Aphids

Soybean aphids are starting
to appear in some soybean fields north of I80 in very low numbers. At these low
levels the beneficial insects can keep the problem in check. Unnecessary
insecticide applications can contribute to aphid outbreaks by killing off the
beneficial insects. The economic threshold for soybean aphids is 250 aphids per
plant.

CORN

Japanese Beetles

In addition to the 3.3” of
rain in my rain gauge near Shueyville in northern JohnsonCounty last Saturday, I found 4 Japanese
beetles. It’s beginning to look like we may have high numbers of beetles in the
areas that have had problems in past years.

Huge numbers of Japanese
beetles have been reported in Illinois
this year. It was reported that a total of 71,984 Japanese beetles were caught
in a single trap in a 24-hour period in Massac county southern Illinois on June 20-21.
The beetles have mainly been a problem near urban areas. The beetles will feed
on soybeans and corn (as well as hundreds of other species of plants), but the
damage to soybeans usually isn’t sufficient to pay for an insecticide
treatment. A general threshold for soybeans is to consider an insecticide if
there is 20% leaf defoliation during the reproductive stages. Most people tend
to greatly over estimate percent defoliation. The pictures in the following ICM
article can help in estimating leaf defoliation: http://www.ipm.iastate.edu/ipm/icm/2002/7-29-2002/soydefoliation.html.

The beetles can cause a
substantial yield loss in corn, since they often feed on the silks, so corn
fields need to be watched closely in the next few weeks in the areas where
Japanese beetles are being observed, such as near Cedar Rapids. An
insecticide should be considered if the beetles are keeping the silks clipped
to within 0.5” of the ear. In past years, much of the silk clipping was done by
the beetles after pollination was complete. It seems like the beetles are emerging
earlier than in the past, which means any silk clipping is more likely to
affect pollination. The beetles will continue to emerge for several weeks and
can live for 30-45 days, so they can continue to cause problems into August.
For more information including pictures of the beetles, see the August 19, 2002
ICM Newsletter at http://www.ipm.iastate.edu/ipm/icm/2002/8-19-2002/jbeetles.html.

FOR YOUR CALENDAR

Midwest Strip Till Conference – July
31, 2007

9 a.m. to 3:00 p.m.

Waterloo

Organized by Research and Extension of IowaStateUniversity, the University
of Minnesota, the University of Wisconsin,
and HawkeyeCommunity College. Manufacturers will demonstrate equipment for
strip-tillage and associated operations, including auto-guidance systems and
fertilizer injectors. Researchers, farmers, and industry representatives
will present the latest information on strip-tillage related topics, including
equipment selection, fertility management, and guidance technology.
Participants will review information booths all day, and lunch is available on
site. This program is free and open to the public. Five Certified Crop
Advisor CEUs (4.5 SW & 0.5 NM) will be available
for a nominal fee. Expo details are at: http://wrc.umn.edu/outreach/striptillageexpo/midwest/index.html

Soybean Aphid and Bean Leaf Beetle Management Tour –
August 8

Management techniques for the
soybean aphid and bean leaf beetle will be highlighted at a tour on the Iowa
Learning farm site on the Rob Stout farm south of West
Chester on Wednesday, Aug. 8. Since first being discovered in the Midwest in 2000, soybean aphids have tended to be more of
a concern in odd numbered years, so this may be more of a pest this year than
last. No-till soybean plots that were planted with and without the seed
treatment “Cruiser” are the focus of research conducted on this Iowa Learning
Farm site. Seed applied insecticides can provide good early season bean leaf
beetle control and also provide some control of soybean aphids, especially when
planting is delayed as it was this spring. Also discussed at the tour will be
value added crop opportunities, including “low lin”
soybeans. A rain simulator will also be demonstrated at the site. A free meal,
courtesy of QUALISOY (http://www.qualisoy.com/) will be
available at 6:30 p.m. followed by the tour. The Iowa Learning Farm project
is a unique partnership of agencies, farm and conservation groups, the general
public and IowaStateUniversity.
Iowa Learning Farm project staff work to increase the adoption of residue
management and conservation practices that are expected to improve water
quality.